1. Field
This invention relates broadly to the field of plant growth and development, particularly to forestry. The invention relates to initiation and promotion of adventitious rooting in plants in general including woody plants, like evergreens, particularly in conifers and in deciduous trees.
This invention also relates to a novel strain of a microorganism which initiates adventitious rooting in plants. Further, the invention relates to a method of promoting adventitious rooting of plants, in particular by co-culturing nonpathogenic bacteria in plants. The invention also relates to a composition, which may but need not include the microorganism, which initiates adventitious rooting in plants and to a method for using the composition to promote rooting in plants.
The invention relates to various tree products, such evergreens obtained from the invention. The invention also relates to various other compositions described further below.
2. Description of the Prior Art
In the United States, forest propagation is primarily seedling based. However, growing seedlings is a slow, labor intensive process, requiring one year in greenhouses and up to four years in outdoor nurseries. Few forest trees, with the exception of poplars and willows and a few others, have ever been vegetatively propagated on a commercial scale. Furthermore, vegetative propagation of conifers, which makes up most of the West's timber supply, is relatively unheard of.
The need for efficient vegetative propagation of forest trees is not limited to the United States, but is world-wide. Japan plants nearly 30 million rooted suji cuttings annually. Europe likewise is seriously concerned about reforestation.
Many of the commercially important tree species, conifers or deciduous, have proven to be difficult to propagate vegetatively by current methods. These hard-to-root plants include the conifers such as pines, spruces, larches, e.g., Douglas fir. Stimulation of rooting has proved to be difficult in mature stocks in vitro cultures in several genera like Celtis, Ouercus, Sassafras, magnolias and conifers. The ability to promote the rooting of recalcitrant tree species, both juvenile and mature individuals, is expected to lead to, in accordance with the invention, the development of new plant products and new markets.
The need to promote rooting is not limited to evergreens like conifers, but applies also to other vegetative plants like deciduous trees, flowering and vegetable plants, and others. It is evident that any plant can benefit from promoting or accelerating of rooting. There is also an important need and commercial importance to promote the growing of plants, e.g., trees which are not so difficult to root, as this promotes an earlier or longer growth period.
In addition to forestry, vegetative propagation is used extensively in horticulture crops, including ornamentals, fruits, nuts, and vegetables. Floriculture is accomplished almost exclusively by cuttings. Many of the world's high carbohydrate vegetable crops, such as potato, yam, sweet potato, and cassava, are routinely asexually propagated.
The following U.S. patents relate to the problem of attempting to induce rooting or vegetative propagation in plants: U.S. Pat. Nos. 5,236,841, 4,353,184, 5,168,059, 5,240,839, 5,059,241, 5,229,114, 4,863,506 and 5,276,005. Of these, U.S. Pat. No. 5,229,114 deals with the use of bacteria to control root nodulation in leguminous plants. Others listed below deal with attempts to induce root formation with chemical molecules. All these patents are incorporated herein by reference.
Several methods have been attempted to stimulate rooting of plants. Dark preconditioning of shoots by covering with black tape has been shown to promote rooting. However, growing these shoots in less than ideal weather, such as in high humidity or during dull weather, results in necrosis and rotting, rather than rooting.
Chemicals, such as auxins, have been proposed to promote rooting of plants. Examples of auxins are indole-3-butyric acid (IBA), indole-3-acetic acid (IAA), and naphthalene acetic acid (NAA). Treatment of plants with rooting hormones frequently produces abnormal roots, which are thick, tubular, and stubby. See FIG. 1. Additionally, the stubby rooted plants, if they survive to grow normally, are delayed in their growth. The precise role of auxins in stimulation of rooting has not been accurately determined.
Other non-auxin hormones have been shown to have effects on adventitious rooting in plants. Cytokinins and gibberellins inhibit rooting. A method to induce adventitious budding consisting of repeated spray applications of trees with cytokinins, followed by treatment with auxins, has been described. U.S. Pat. No. 4,353,184 (Abo El-Nil). A method to promote somatic embryogenesis in tissue culture using repeated treatments with abscisic acid, a hormone believed to promote rooting through its antagonistic action to cytokinins and gibberellins, has been described. U.S. Pat. No. 5,236,841 (Gupta). None of these chemicals have been found to be fully satisfactory or have found acceptance on a commercial scale.
Different species of fungi have been described which produce auxins and other plant hormones and which may promote rooting by providing these hormones.
Stimulation of adventitious rooting in plants by co-culturing with bacteria has been described in many plant species. Adventitious roots formed and somatic embryos were regenerated from soybean (Glycine max L.) nodular calli induced by co-cultivation of cotyledonary explants with Pseudomonas maltophilia. However, pathologic effects of P. maltophilia were observed, the parent callus growth was inhibited or the callus died.
The bacteria, Agrobacterium rhizogenes, transforms the genome of its host plant which then carries the Ri gene of A. rhizogenes. Although transformed plants have increased root weight, they have decreased shoot weight when compared with normal non-transformed plants. The shoots produced from transformed plants are altered, and flowers are smaller compared to normal plants. Additionally, the root systems of plants infected with A. rhizogenes are altered, often to the extent that the altered root condition is referred to as hairy root disease. Although A. rhizogenes has been used effectively, although inconsistently, to promote rooting, it is uncertain to what extent the transformation of the host plant's genome can lead to deleterious effects.
Similarly, Agrobacterium tumefaciens induces rooting but causes crown gall disease.
It is evident that bacteria have not as yet proven satisfactory to promote root induction and growth of plants.
From this review of the literature and patents it is apparent that a world-wide serious need exists relating to propagation of plants, in general be it deciduous trees, ornamentals or crops, or in particular trees like conifers to promote initiation of adventitious rooting systems without causing pathology. This need has been addressed for many years. It is noteworthy that none of the solutions proposed have been found to be entirely satisfactory.
This invention contributes to solving this world-wide need, a need that is becoming increasingly serious because of industrialization and the awareness of the world's limited natural resources.
In view of the lack of success of the reported work in promoting healthy rooting systems in plants, in particular, with various bacterial systems, the findings, and success with bacteria in accordance with the invention are particularly unexpected.
The bacteria discovered in accordance with the invention have been designated as Root Stimulating Bacteria (RSB).